The following figures give achievable S/N ratios (where N is r.m.s.
noise) in one hour integrations when observing with an intermediate modulation
frequency of 143 Hz. The S/N for different resolutions is proportional
to .

Note that under detector noise limited conditions (appropriate where the
slope of the lines in the figures is 1) the S/N is improved by a factor
of approximately two when a modulation frequency of 20 Hz is used.